John Wesley on 1 Samuel 13:20

Philistines - Not to the land of the Philistines, but to the stations and garrisons which the Philistines retained in several parts of Israel's land, though Samuel's authority had so far over - awed them, that they durst not give the Israelites much disturbance. In these, therefore, the Philistines kept all the smiths; and here they allowed them the exercise of their art for the uses following.